Normally-off 4H-SiC trench-gate MOSFETs with high mobility

A new 4H-SiC trench-gate MOSFET structure with epitaxial buried channel for accumulation-mode operation, has been designed and fabricated, aiming at improving channel electron mobility. Coupled with improved fabrication processes, the MOSFET structure eliminates the need of high dose N+ source implantation. High dose N+ implantation requires high-temperature (>= 1550 degrees C) activation annealing and tends to cause substantial surface roughness, which degrades MOSFET threshold voltage stability and gate oxide reliability. The buried channel is implemented without epitaxial regrowth or accumulation channel implantation. Fabricated MOSFETs subject to ohmic contact rapid thermal annealing at 850 degrees C for 5 min exhibit a high peak field-effect mobility (mu(FE)) of 95 cm(2)/V s at room temperature (25 degrees C) and 255 cm(2)/V s at 200 degrees C with stable normally-off operation from 25 degrees C to 200 degrees C. The dependence of channel mobility and threshold voltage on the buried channel depth is investigated and the optimum range of channel depth is reported. (c) 2008 Elsevier Ltd. All rights reserved.